Validation Help

Hi all, I got this error :

element “article” undefined
<article class=”text css3-3 1″>
?
You have used the element named above in your document, but the document type you are using does not define an element of that name. This error is often caused by:

incorrect use of the “Strict” document type with a document that uses frames (e.g. you must use the “Frameset” document type to get the “<frameset>” element),
by using vendor proprietary extensions such as “<spacer>” or “<marquee>” (this is usually fixed by using CSS to achieve the desired effect instead).
by using upper-case tags in XHTML (in XHTML attributes and elements must be all lower-case).

I think the error from this code :

div class="container personal">
<img src="https://kreatifbuzz.com/template/cat_personal.png" alt="Category Personal" width="258" height="96"/>
<<strong>article class="text css3-3 1</strong>">
<a href="https://kreatifbuzz.com/category/personal/" target="_blank"><img src="https://kreatifbuzz.com/template/cat_personal_hover.png" alt="Category Personal" width="258" height="96"/> </a>
</article>
</div>

<div class="container tutorial">
<img src="https://kreatifbuzz.com/template/cat_tutorial.png" alt="Category Tutorial" width="258" height="96"/>
<article class="text css3-3 2">
<a href="https://kreatifbuzz.com/category/tutorial-kreatif/" target="_blank"><img src="https://kreatifbuzz.com/template/cat_tutorial_hover.png" alt="Category Tutorial" width="258" height="96"/> </a>
</article>
</div>

the css for that code :

.container{
	position:relative;
	overflow:hidden;
	height:96px;

	 -webkit-transition: all .5s ease-out;
	 -moz-transition: all .5s ease-out;
	 transition: all .5s ease-out;
}
.container:hover{
	cursor:pointer;
	-webkit-box-shadow:0 0 0px #000;
	-moz-box-shadow:0 0 0px #000;
	box-shadow:0 0 0px #000;
}

.text{ height:auto;width:inherit;
 position:absolute;
}
.text a{width:258px;  display:block;
}

article.css3-3
{
 right:-258px;top:0;
 -webkit-transition: all .5s ease-out;
 -moz-transition: all .5s ease-out;
 -o-transition: all .5s ease-out;
 transition: all .5s ease-out;
 width:258px;
}
.text a.css3-3{
 -webkit-transition: all .4s ease-out;
 -moz-transition: all .4s ease-out;
 -o-transition: all .5s ease-out;
 transition: all .4s ease-out;
}
.text a.css3-3:hover{
 color:#d0206a;
 text-decoration:none;
}
.container:hover article.css3-3{
 right:0;
}

so, how to remove the “element “article” undefined” error?

this is my blog – kreatifbuzz.com